Construction median barriers are employed in many diverse applications. Perhaps most often, however, and as the name would suggest, these barriers are used for demarking the medians of roadways while road construction is under way.
A number of different types of couplings have been used in these applications in order to allow the coupled barriers to better withstand vehicular impacts, and to apportion impact energy between the vehicle, the impacted barrier panel and those panels to which it is connected. In order to function properly, these barriers must be coupled with one another in such a way as to safely communicate impact energies along the length of the coupled structure. Couplings have been assessed in terms of their resistance to the loading conditions, which describe the four major force components which may result from vehicular impact against the barrier.
The first loading condition involves the tensile forces that are applied through the connection along the common longitudinal axis of two longitudinally aligned, interconnected barrier panels. The second loading condition is a measure of the shear forces acting normally to the longitudinal axis and generally parallel to the ground. The third load relates to a rotational moment acting across the longitudinal axis and generally parallel to the ground. The fourth loading condition is in relation to a torsional moment acting around the longitudinal axis.
Two of the strongest coupling designs in use today are the so called New Jersey Welsback interlock connection and the slightly weaker New York "CI" interlock system. Both couplings include female members having a "C" shaped cross-section, formed by an opening along one side of what would otherwise be a generally rectangular cross-section. This opening is designed to accommodate the shank of a male member, such that the larger, free end of the male member is locatable within the interior of the "C" section, while the shank extends out through the above mentioned opening. In this way the male member is secured in interfitting relation within the female member.
In the case of the New York "CI" interlock system, barriers are made up of panels having two mutually opposed, female ends. Adjacent ends are secured to one another by driving a pin, having an "I" shaped cross-section between adjacent female ends of two panels aligned with the openings in the "C" sections in register with one another. The shank of the pin passes through the openings of the two female coupling members, with the larger free ends thereof then being secured against axial withdrawal by the narrowness of the opening. Although the system is relatively easy to install, and removal of individual panels is a straightforward operation that does not require moving any more than the panel in question, the three part system is inherently disadvantageous. This problem has been overcome in a design that has been adopted in Ontario, wherein each panel has both a male and a female end. In either case, the tensile forces applied in the axial direction, as mentioned above, act against little more than the remainder of the sides in which the opening was cut. As a consequence the resistance to such forces in the New York device, were found to be about half of the resistance of the Welsback device. In the latter, the 37 C" section is deeply recessed within the cement panel, so that the axial forces act against substantially more supporting material than is available in the case of the New York device. This deep recessing, and the requisite lengthening of the interfitting male member, may account for why testing has shown the Welsback device to have a some what lower resistance to shear stress than the New York device. In addition, the Welsback device employs a female member that is much more complex and more expensive to manufacture.
There remains a need for strong, simple and relatively inexpensive couplings, particularly in construction median barrier applications.